Midterm 1 - Version B - Short Answer -...

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Unformatted text preview: Psychology 60 – Spring, 2010 – Midterm1 – Given 4/20/10 1 Short Answer / Computation Questions:
VERSION B For these questions, you must show your work in order to receive any credit. If you are using a
formula to solve the question, write the formula first, and then apply the formula to the problem.
Write legibly and CIRCLE your final answer for each question
1) A market researcher interested in how much individuals on the UCSD campus talk on their
phones takes a sample of 6 students and asks them to report how many minutes a day they
talk on their phone. The following are the data this researcher obtains:
40, 83, 60, 6, 18, 27
a. Find the value of SS for this sample. Xbar = 234/6 = 39
X
40
83
60
6
18
27 X-Xbar
1
44
21
-33
-21
-12 (X-Xbar)2
1
1936
441
1089
441
144 Σ(X­Xbar)2 = 4052 X
40
83
60
6
18
27
Σ = 234 Or , 13178 – 2342/6 = 4052
b. Assume that SS = 4100 (DO NOT USE ANY OTHER VALUE FOR SS).
Find the best estimate of the standard deviation of the population
estimated σ = sqroot( SS/(n­1) )
estimated σ = sqroot (4100 / 5 )
estimated σ = sqroot ( 800 )
estimated σ = 28.64
X2
1600
6889
3600
36
324
729
Σ =13178 Psychology 60 – Spring, 2010 – Midterm1 – Given 4/20/10 2
2) In a population of exam scores, a score of X = 90 corresponds to z = +2.00, and a score of x = 81
corresponds to z = ‐1.00. Find the mean and standard deviation of the population.
μ = 84 σ = 3
3) A research firm is interested in obtaining a sample of individuals who use Facebook a “typical
amount of time per day,” which they specifically define as the middle 34% of people in terms
of hours spent per day on the website. Assume that Facebook usage in terms of hours per day
is normally distributed with μ = 4.5, and σ = 1. Determine the cut‐off values in number of
hours per day that this research firm should use in recruiting subjects.
p( ‐0.44 < Z < 0.44 ) = .34
Xlower = 4.5 + (‐0.44)(1) = 4.06 hours
Xupper = 4.5 + (+0.44)(1) = 4.94 hours
...
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